CHENNAI: One could apply basic logic to assume that air pollution levels in metropolitan cities must have reduced, owing to the nationwide lockdown. Well, most of us did receive on WhatsApp, the satellite image of Wuhan city, completely cleared of nitrogen dioxide (NO2), due to the shutdown.
However, Chennai’s monitors installed by the Central Pollution Control Board (CPCB) have surprisingly shown no significant difference in pollution levels. Urban Sciences, a Mumbai-based start-up, analysed the city’s air quality data during the first and last week of March (before and after the lockdown came into effect), and found that pollution levels had hardly varied. “This seems to indicate that locations being monitored here are essentially capturing background levels, and not the actual sources of pollution,” said Ronak Sutaria, CEO of Urban Sciences.
Chennai also has the lowest number of monitoring stations (four) among all metropolitan cities in India. Data from these stations - Alandur, Manali village, Manali and Velachery - is also not calibrated. That’s odd! For instance, the city’s only PM10 monitor recorded 134 and 203 ug/m3 on March 29 and 30 (during the lockdown with minimal vehicular movement), as against the permissible 100. Also, NO2 levels (of which the main source is fuel combustion) at Velachery was recorded under 5 ug/m3 for 581 hours.
“This data is unusable as it does not capture any pollution source information,” said Nakul Mehta of Respirer Living Sciences. Velachery, being one of the busiest areas, cannot record levels below 5, he added. A senior official of the State Pollution Control Board said that four monitoring stations were not enough. “We have installed real-time monitors in Perungudi, Kodungaiyur, Koyambedu and Royapuram. Those inputs when integrated with data from CPCB stations, will generate a more realistic air quality index,” he added.
Background pollution
Background concentration is the lowest level of ambient air pollution to which the population is chronically exposed, and is not affected by local sources. Hence, the readings suggest that monitors are not effective enough to capture pollutants during normal days.